The overriding focus of this research program rests upon the question of just what does a child gain control of when he learns or mis-learns the sound system of his language. The central thesis is that the "just what" is a highly organized and intricate phonological system. The goal of the project, then, is to explicitly describe (and compare) the linguistic organization of the sound systems of both normal and speech defective children. The primary objectives are 1) to study the linguistic organization of the normal developing sound (phonological) system of children beginning with the onset of talking and continuing to approximately three years (by analyzing longitudinal speech samples collected from children starting with the first words at about 12-14 months), 2) to describe the linguistic organization of the sound system giving rise to deviant speech patterns of children who have failed to develop normal speech - also taking into account the analyses of the normal developmental data which will serve both as appoint of comparison and reference in defining "defective" or abnormal - (by analyzing the articulatory error patterns of five and six-year old children with severe articulatory disorders), and 3) to investigate the clinical applications of these linguistic analyses (generative phonology) to the diagnosis and treatment of children with articulatory disorders (by tailoring individual therapy programs for each child based upon his own deviant system of speech.